Skin Test for Allergy
Syed Shahzad Mustafa, MD
After growing up in the Rochester area, Dr. Mustafa pursued his undergraduate studies at the Johns Hopkins University in Baltimore and attended medical school at SUNY Buffalo. He then completed his internal medicine training at the University of Colorado and stayed in Denver to complete his fellowship training in allergy and clinical immunology at the University of Colorado, National Jewish Health, and Children's Hospital of Denver.
Allison Ramsey, MD
Dr. Allison Ramsey earned her undergraduate degree at Colgate University and her medical degree at the University of Rochester School of Medicine and Dentistry. She completed her internal medicine training at the University of Rochester School of Medicine and Dentistry and remained at the university to complete her fellowship training in allergy and clinical immunology. Dr. Ramsey is board certified in internal medicine and allergy and immunology. Her professional interests include the treatment of drug allergy and eosinophilic disorders. She also enjoys teaching medical trainees. She is a member of the American Academy of Allergy, Asthma, and Immunology, the American College of Allergy, Asthma, and Immunology, the New York State Allergy Society, and the Finger Lakes Allergy Society. In her personal life, her interests include exercise, especially running and horseback riding; and spending time with her husband and two children.
John P. Cunha, DO, FACOEP
John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.
What is a skin test?
A skin test is a test done on the skin to identify if a substance (an allergen) is potentially triggering an allergic reaction. Environmental allergens (aeroallergens), including furry animals, dust mites, tree pollen, grass pollen, weed pollen, and molds can cause allergic eye symptoms, nasal symptoms, and asthma symptoms. Allergens that can trigger allergic reactions involving the skin, respiratory system, gastrointestinal system, and cardiovascular system include foods, medications, latex, and insect venoms.
How is an allergy skin test done?
Allergy skin testing is noninvasive and generally very well tolerated, even by small children. A small amount of the suspected allergy-provoking substance (the allergen) is placed on the skin. The skin is then gently punctured through the small drop with a special sterile puncture device. An allergy skin test is also called a prick/puncture test. The older terminology was "scratch test." With venoms, certain medications, such as penicillin, and in certain cases with aeroallergens, a second step of testing involves injecting a small amount of the allergen into the skin with a small needle. This is called an intradermal or an intracutaneous test. This type of testing should never be performed for foods.
What is a positive skin test result?
A positive skin test involves the formation of a bump (wheal) and redness (flare). In addition to the allergens in question, skin testing is also performed with a positive control (histamine) that should always cause a skin reaction, and a negative control, (saline), that should not cause a reaction. A test is positive if the allergen causes a wheal 3 mm greater than the negative control, and if the skin has a response to the histamine, as well. It is important to know that individuals cannot undergo skin testing if they are using antihistamines, since this blocks the histamine-mediated reaction.
For example, if a specific food allergy is suspected, a skin test uses a dilute extract of the suspected food. A small drop of this particular liquid extract is placed on the skin of the forearm or back. This underlying skin is gently punctured through the small drop with a special puncture device. The test is positive if there is a wheal and flare response described above. A positive test raises the possibility of a true allergy but is not diagnostic or confirmatory for having a true allergy. If there is no reaction with a wheal and flare, the test is read as negative and being allergic is very unlikely. If the skin test is positive, it implies that the patient has a type of antibody (IgE) on specialized cells in the skin that release histamine to cause symptoms of an allergic reaction. These cells are called mast cells and the IgE antibody bound to them is specific to the food being tested, like a puzzle piece. It is important to note that a positive skin test does not automatically mean a person is allergic to a food, medication, or aeroallergen. The skin test is one component of the information an allergist uses to make an accurate diagnosis, but the most important information comes from the patient's reported symptoms.
Allergies & Asthma
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